Adders – Part  Two

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Defence and escape

If you disturb the snakes, you will find out the differences between the two species in defence and escape behaviour.  If several adders are basking together, you will also find out whether some are more wary than others.  When they are coiled up together they seem to change their positions without any problems, though you might wonder whether they known which bit belongs to which snake.

Locomotion

Snakes can glide along using the large scales underneath, which are controlled by individual muscles along the body.  In fact, every scale on the body is connected to a muscle.  Muscles connect ribs to ribs, ribs to scales, and scales to scales, giving snakes great control over their movements.  In the gliding movement, the snake produces a wave-like motion; each scale in turn is lifted, moved forward, lowered, and moved back in a slightly different phase from the next one.  A gliding snake is rather like a centipede in a sack race.  It is also analogous to the ultrasonic motor that is found in some camera lenses.  Snakes have evolved an enormous number of ribs, which help to anchor some of the muscles.  Click here to see how an ultrasonic motor works.

If you see a courting male, gliding partly on the ground, and partly on the moving female, you can only marvel at the coordination required.  Imagine trying to walk with one foot on an escalator and the other on a stationary stair.  Then imagine that you are a centipede trying the same trick.

Snakes can also make use of objects by pushing the curved body against them and creating a wave down the body.  This can be understood by imagining a large screw with a very coarse pitch, rotating and passing through a nut.  The serpentine motion of a snake is like a two-dimensional projection of a screw.  It is also analogous to swimming, as seen in a sea-snake, eel or leech, except that the "medium" is discontinuous and rigid.

An extreme case of this is side-winding, in which the snake creates its own series of obstacles by pushing into the sand or soil.  The snake actually forms a a helix which is very flat in the vertical dimension.  So a side-winder has a handedness.  Do all side-winders have the same handedness?  Snakes and slow-worms that cannot side-wind can experience difficulty on a powdery surface, and may even be unable to progress.

In water, many snakes can swim like an eel, and the sea-snakes are so well adapted that swimming is all they can do.

The pictures above, some of sloughed skins, show the large ventral scales.  If a snake gets into a place where it cannot go forward, it can in fact glide backwards, though less efficiency than when going forward.  Although the scales are designed for grip in the forward direction, an adder can go down a rock sloping at about thirty-five degrees, but in going over the edge, it will eventually fall off when the weight of the hanging part is too heavy for the part on the rock.  Adders don’t seem to mind falling six or nine inches on to grass.  After all, they are flexible, they have no long bones to break, and they have elongated organs which are unlikely to be jerked around as ours would be.

Click here to download or run in place a short simulation of the motion of the scales.

On a smooth hard surface, such as a shiny tarmac road, or on a very powdery one track, a snake or a slow-worm may become trapped.  By putting a stick where the animal can push, you can help the animal can make progress.  This action can be repeated until safety is reached.  Use a long enough stick, so that the animal cannot bite you.

Click here if you want to skip a section about the physics and maths of movement.

The shapes that snakes make are as varied as the terrain over which they pass.  But they are obviously not any old shape.  If you try to draw a snake, some curves will look more realistic than others. The curve shown below is an idealized one calculated on the assumption that the curvature varies sinusoidally along the snake.  Real examples would be less regular because of constraints imposed by the surroundings.  A young adder will sometimes adopt this position when threatened, because when curved, it can strike by straightening out.  A straight snake cannot strike forward, any more than a boxer with arm outstretched.

In the uniform medium of water, an eel, a sea-snake or a large leech illustrate the elegant curves that can be seen in nature.  The grass snake is a good swimmer, and can sometimes be seen in a pond or a canal.  

A somewhat similar curve may be seen when certain snakes hang from trees, waiting for prey.  The excess length in the curves can be used to unleash a strike.  In this case, the curves would be slightly modified to cope with the downward acting weight.  

A snake lying in a straight line, flat on the ground and facing you, has no way of striking.  But the spitting cobra can still get you, as its name suggests, even when out of biting range.  The fangs point forward, and two streams of venom are ejected, probably at your eyes.

The snake does not do any calculations in moving, but the point is that its curvature varies in a simple manner.  The actual curves of a snake makes are likely to be such as to minimise the average curvature along the length, which probably minimizes muscular energy.  Flying snakes can even flatten the body into a wing, with which they glide.  Stability is gained by a wave which passes down the body, probably helping to adjust the angles of the body in response to the movements of the snake and the air.  Landings are probably fairly heavy, but if you have no limbs to break, and your organs are spread along the body instead of being in heavy lumps, this probably does not matter.

By making a few small changes in the computer program, a more realistic shape can be created, as we see in the diagram at left.

Who would have thought that success could come to an animal which looks rather like a head joined to a long tail, or a head with a long neck, or a finger with a head on it?

These two pictures show a Bowden cable, in the first example, lying on a linoleum floor, and in the second, shaped by panel pins in a piece of cardboard.  In both cases, the physical rules are simple to state, but the mathematical expression of the curves is more complicated.

The next diagram shows an elastic object like the Bowden cable with five different shapes, all governed by the curvature varying as a power of the sine of the position along the object.  All the curves have the same length and fit into the same space per wiggle.  The black curve corresponds to the plain sinusoidal variation that has been used so far.  The numbers correspond to the elastic energy; the black curve has less than the others, though not by much.  The green curve has long sections with not much curvature, but these are more than compensated by the highly curved parts.  The red curve errs in the opposite direction.

Curves of lower energy can be created for the same length and the same two end points by using fewer wiggles, at the expense of requiring a bigger enclosing area.

This minimum in energy is only a local one in the parameter space.  The curve that gives the least energy is obtained for a given length between two points is a single arc, which is unlikely to occur in the case of a snake, because it is normally trying to go in a particular direction.  Another solution, in three dimensions, is a helix, which is better than the curves above, but worse than the single arc.

Although the black curve above is close to the minimal energy for the family of curves shown, it is unstable against a general bending.  A steel wire with loosely pinned supports would spring out into the arc with only a half a wavelength.

These curves may be related to electric and magnetic lines of force, which in the nineteenth century were considered to depict the properties of an elastic medium, the luminiferous ether.  Certainly, in the vicinity of the sun, magnetic lines of force writhe around like the snakes on the head of the legendary Medusa.  And in string theory, mathematicians have created tiny lines in space which can oscillate.

In the past, progress in understanding has sometimes been held up by an insistence on simple mathematics instead of simple physics, as in the case of planetary orbits.  Understanding only began when the revered circular orbits were very reluctantly abandoned by Kepler in favour of elliptical ones, though Kepler did not know the reason for the ellipses.  But then, the only reason for the circles was the belief that they were somehow ideal.  More progress was made when Newton formulated simple physical rules that led naturally to the hitherto incomprehensible ellipses, and unified the behaviour of astronomical and terrestrial objects.  More general methods such as the use of the Lagrangian unified physics even more, at the cost of almost complete abstraction from any particular system.  More about this type of subject can be found in Nature’s Maths and in Numerology.

Physicists still believe that nature ought to be simple, and they prefer simple ideas to complicated ones.  The problem is – what is the right kind of simplicity?  And simplicity of ideas doesn’t mean simplicity in working out the consequences.

Here are two pictures made using a flexible plastic ruler, a bulldog clip, and a flat-bed scanner.  They are very smooth curves, generated by a simple rule about bending moments, yet they are not circles or ellipses, or any other simple curve that you might learn about at school.

Below are two versions of a snake descending a staircase.  Clearly both are absurd.  The real picture would lie between the two extremes, again, to minimise energy.

This picture hints at the minimising of energy.  The adder could ride stiffly over the rocks, keeping its body almost straight, but this would mean raising parts of its body higher than necessary, wasting muscular energy.  The adder could make its body conform closely to the rocks, but this would use more energy in bending.  The graceful curves we see are the result of the best compromise between minimising energy and speed of progress.  What a wonderful contrast between the curves of the adder and the hard shapes of the rocks.

Here we see a completely different constraint on movement:  the links of this chain, like the vertebrae of a snake or a slow-worm, cannot attain angles with their neighbours outside a certain range.  The maximum angle expresses itself visibly as a minimum radius of curvature.

If you don’t believe that maths has much to do with nature, try one or more of these three books.

Many topics about nature’s mathematics are discussed in Professor Ian Stewart’s exciting book "Nature’s Other Secrets" – Penguin – ISBN 0 14 025876 0.

An older but beautiful book is "Patterns in Nature" by Peter S Stevens – 

Peregrine – ISBN 0 14 055 114X

An even older, but deservedly famous, book is "On Growth and Form" by D’Arcy Wentworth Thompson, who was ahead of his time with his many insights.

We don’t have to know maths or physics, to finds things beautiful, but some things are not comprehensible without this knowledge.  If we find some animal or plant ugly, it may be that we don’t know what it is trying to do.  People sometimes use a charging rhino as a symbol of insensitivity, but if you see a trotting rhinoceros at a large zoo, you will see a grace matching that of any dancer, because it wastes energy minimally.  Dancing in fact, like some other arts, is an artificial attempt to achieve what is done quite naturally by other species.

If we look at tiny creatures like daphnia or aphids, or at floating creatures like jellyfish, we see what happens when gravity is not a constraint.  The same sort of thing happens in the design of spacecraft such as the lunar landers, which look a bit like huge insects, though they do have to withstand the accelerations and vibrations of take-off.

And this hints at the reason why even the best simulations of animals such as dinosaurs still don’t look quite right.  They won’t look right until the algorithms for motion are based on mass distributions, forces and energy, as well as on smooth curves.

And it hints at the basis for "jizz", which is the term that bird watchers use to label the sometimes indefinable feeling that they have identified a bird from a brief glimpse.  They are not cheating – they have picked up subtle clues.  The curves formed by adders, grass-snakes and slow-worms, for example, are slightly different in character.

Perhaps this is why taxidermy is so difficult.  In a sense, a picture or even a cartoon can capture the essence of a living thing more accurately than a stuffed animal:  the art is not more accurate, and we are not fooled into thinking it is alive, but it can somehow capture what matters.

Many years ago, when snakes were more common in Britain, you could go to a certain place in Swindon, and be almost sure to see a number of grass-snakes, lined up along the edge of a field.  Each one would be coiled up in neat, tight spiral near its hole.  When disturbed, they would smoothly unwind the spirals and disappear down the holes.

This aerial view of Paris shows the serpentine path of the Seine.  Like the curves of a snake, it does not follow any of the simpler mathematical curves, having evolved over many years by physical processes.  In fact, the course of such a river, free from concrete banks, slowly moves, as mysteriously as a side-winding snake, to the despair of map-makers and land-owners alike.  Sometimes the river may make a short-cut, leaving behind an ox-bow lake, marking its previous course, as the side-winder leaves its mark in the sand.  We cannot see this happen, except in a computer simulation, but we can see the elegant motion of a side-winder or a swimming snake.  If we try to straighten the course of a large river, we may experience problems, because we are forcing a large mass of water, with huge momentum, to deviate from an optimal evolved course.

In some high places in Gloucester, while you are watching adders, you can look around and see glimpses of the river Severn snaking across its flood plain on its way to the Bristol Channel.

As snakes, and indeed slow-worms, have evolved from animals with legs, their ancestors must have gone through stages in which the legs gradually disappeared.  Indeed, some pythons possess vestigial limbs.

At some stage, the number of ribs increased greatly, and the muscles in that area of the body must have developed, along with the ability of the nervous system to control them.  

If you watch the graceful movements of a pair of adders, or of two males gliding along while competing, you will see that the control and coordination is as perfect as that of any other animal.  Some snakes can even glide down from high in the trees.

So the brains of lizards and snakes, while having a common ancestry, must have developed quite differently in the relative complexity of the parts controlling the legs and the rib areas.

Another bit of maths concerns a snake, such as a cobra, that rears up to defend itself.  It needs to minimise the forces at each point in its body.  An old mathematical problem suggests the answer.  It is about a pile of bricks, which are overlapped to produce the maximum possible overhang.  If you neglect practical considerations such as imperfect rigidity of the bricks and of the foundations, you can show that the Nth brick from the top is overlapped by one Nth of its length.

You only have to smooth out the jagged edges and add a head, and you have the shape of a cobra, though you might well object that the curve should be the other way up.

If you don’t believe in maths, consider Torvill and Dean.  What was it that made them so different from all the others?  Couldn’t it have been a smoothness of motion, and a minimising of energy, and a continuity between each movement and the next, that none of the others had achieved.  Mathematically this would be described in terms of continuity of differential coefficients.   Ballet dancers, figure skaters and gymnasts have to put in an enormous amount of training in order to perfect movements which are not natural for homo sapiens.  Much of what we admire in the movement of animals is the result of millions of years of evolution, resulting in a good compromise between all the competing demands on the system.  

In a sense, we humans are not exceptionally good at any one physical activity, and even what a few individuals can do with immense effort can be achieved with ease by one species or another.  But the human species is very adaptable, like the feral pigeon, the house sparrow, the house fly, and other ubiquitous species.

Many people admire the skills demonstrated by world-class skaters, skills which are acquired through dedication and hard work.  The performance of athletes, dancers, skaters and swimmers can be bettered by many kinds of animals, because the animals have evolved to perform in specialist ways.  Do more people admire the sinuous movements of snakes or of skaters?

In a very dense and slippery liquid the waves would be stationary with respect to the liquid.  In practice, with real liquids, there is some slippage.  To see how the system works, click here for a computer simulation, and choose "Run in the current location".

The same idea can be used on land.  On a smooth surface with a few scattered obstacles, a snake can bend a part of its body to touch each obstacle, and then move the waves along its body, pushing itself along.

Some surfaces are very difficult for snakes and slow worms.  Loose sand and shiny roads can leave an animal stranded.  Some species of snakes have adapted to sand by developing side-winding.  In this method, the snake creates a series of furrows and ridges in the sand, and uses these to create purchases for the waves.  The snake makes not only horizontal waves, but vertical ones, of small amplitude, just enough to push the body into the furrows, and to raise the rest of the body slightly off the  ground.  The two sets of waves are not in phase.  The snake is in a sense a flattened roller, and is not required to obtain purchase with it scales in order to progress.

Note that the wave is essential: if you draw a wiggly snake at forty-five degrees to the axis of a sheet of paper, make the paper into a cylinder and roll it, the snake moves at right angles to the axis of the cylinder.  There is nothing wrong with that, but the problem is that half of the snake is upside down at any time.  Even that is not in itself a problem: no, the real problem is that the head is rotating, and is upside down and sideways much of the time.

No doubt the vision of a snake could have evolved to cope with this, but the brain might have been bigger, and the difficulty of recognising threats would be great.  The sidewinding method undoubtedly wastes more energy than simply rolling, but the snake’s head takes no part in the wave motion, and points in the required direction all the time.  No part of the snake is ever upside down, or in fact more than slightly sloping.

To create a simple roll, the snake would have to continually distort the cylinder to create an imbalance, otherwise it would never move, so even rolling is not energy free.  Going up a slope would probably be very difficult by pure rolling.

Click here to see a simple computer simulation of a side-winding snake.

Here is a part of a frame from the simulation.

Do all snakes side-wind in the same way, or are some left-handed and some right-handed?

The motion of the side-winder is both elegant and fascinating.  Like the swimming snake and the sinuous snake, the side-winder produces forces that are not entirely in the direction of motion.  In this it resembles the wing of a bird or an aircraft, or the sail of a boat.  These aerofoils produce forces which are predominantly at right angles.  Indeed, a high performance glider may need to overcome drag which is as little as one sixtieth of the lift.

The sidewinder, the gliding eagle, and the sailing ship are using rotation, yet none itself rotates.  The snake is creating a rotating shape, while the wings of the bird and the sails of the ship are producing a rotation in the air which is analogous to that produced by a top-spun table-tennis ball..

The motion of the side-winder is both elegant and fascinating.  Like the swimming snake and the sinuous snake, the side-winder produces forces that are not entirely in the direction of motion.  In this it resembles the wing of a bird or an aircraft, or the sail of a boat.  These aerofoils produce forces which are predominantly at right angles to the motion.  Indeed, a high performance glider may need to overcome drag which is as little as one sixtieth of the lift.

Some snakes can even glide, albeit steeply, by flattening their bodies into a rather thick aerofoil, and adopting a sinuous shape which presents much of this aerofoil at right angles to the wind.  The snake slowly moves the wave along the body, probably to increase control and stability.

Not bad – sliding, side-winding, swimming and gliding, in a creature with no limbs.  In fact, no creature without wings or fins is able to glide at a shallow angle.  Human attempts to create aircraft without separate specialised wings and fuselage have been few, and most were experimental aircraft.

When to see adders

When can you see adders?   The season is rather variable, because it depends on the weather.  You can be lucky enough to see an adder as early as St Valentine’s day, and you may see one eight months later in mid-October.  And these are not the extremes – during very mild winters people may, rarely, see adders in November, December or January.  They are not fond of high temperatures,  and are in fact found further north than any other reptile – as far north as the Arctic circle, and at altitudes up to about 3000 m in the Alps.

If the warm sun forces you to discard too many clothes, most of the adders will have stopped basking because it is too hot.  But if you are wearing a pullover and an anorak because it is cold, they probably won’t have come out.  As a rough guide, 10 degrees to 16 degrees is about the right range.  But adders, like people, differ considerably in their behaviour, and you can sometimes find one adder that is out when all the others are in.  You can sometimes discover the presence of adders by finding the sloughed skins – inside out.

Behaviour of adders

The behaviour of adders depends on other factors beside the temperature.  They can use shade from the sun and they can shelter from the wind.  Once out, they may be quite reluctant to go in.  Sometimes an adder will even stay out during a shower of rain.  Don’t forget that some heat and light can get through thin cloud.  If the sun is not warm enough, an adder can flatten its body to maximise the exposed area, as in the middle of the next photograph.

Much more rarely, an adder will turn a part of its body on its side to expose the large dark scales on its underside, to absorb more heat.  These large scales are used by the adder in moving.  The adder can go down surprisingly steep slopes on rocks, but if decides to go over the edge of a very steep slope, when about half the adder has gone over, it will lose control and fall off, landing in a heap on the grass below.  If you try to follow an adder, crawling on your knees with a camera over rocks, thistles or brambles, you will find out how much better the adder is than you are at getting around in this terrain.

Underside of adders

The pictures below show the large dark under-scales, two of contesting males, and one of an adder exploring a cavity in some rocks.  In the second picture the shiny scales have reflected the flash-light.

If a snake cannot progress further forward, for example in a blind hole, it can use these wide scales to go backward, though not as well as it goes forward.

The next two pictures show portions of cast skins, under side and upper side respectively, flattened out, while the remainder show pictures of skins as sloughed.

The sloughed skin shows no sign of the normal dark colour of the under side, and in fact is almost transparent there, but the upper side has retained the pattern well.  Do you think that the pattern of the new skin will be the same as the pattern of the old one?

Here are pictures of some adder scales.  Each one has a ridge from front to back, like the scales of the grass snake Natrix natrix, but unlike those of the smooth snake, Coronella austriaca.  Note, in the second and third pictures, how the flexible skin between the scales allows expansion on the outside of the curve.  This ability to expand is essential when large prey is swallowed.  Actually, some of the expansion is probably achieved by smoothing out folds in the skin.

The ridges can be seen in this picture of part of a sloughed skin.  When the time approaches for an adder to shed its skin, the old layer separates from the new one underneath.  The eye often seems to be occluded by a bluish colour.  Eventually the skin splits at the head, and the adder uses friction against plants to help the skin to peel back inside out in one piece.  Every detail is visible in the old skin, including the round scales that covered the eyes.

Looking at the pattern of scales on a snake, a lizard, or a pangolin, you might be reminded of the pattern of a long pine cone.  But there is a fundamental difference.  The animal patterns have left-right symmetry: the plant ones do not.  The numbers of left spirals and right spirals in a plant are different, as a result of a physical difference between the plant and the animal.  The asymmetry is clearly visible in the picture.  In a plant, all the parts grow from a small region – the meristem: in a reptile, all the scales are present from the start.  To find out how this difference affects plant growth, click here.

Feeding

You might expect sometimes to see a snake with a swelling after it has swallowed a small animal.  You might wait a long time.  By the time that a small mammal has had the air squeezed from its lungs, had its rib-cage squashed, and had its fur pressed down to its body, it doesn’t occupy anything like the volume that the live animal seems to occupy.  If the prey is a small lizard, you certainly won’t see any sign of it.  We must remember that a great many animals take smaller prey than we might imagine.  We may think of foxes in terms of chickens and lambs, but much of the time they have to make do with things like grubbed up beetles.  In the case of a snake, small invertebrates are taken.  Adders do not need to eat many times during the summer, because they live rather inactive lives.

Contrast this with the life of the shrew, which must eat voraciously just to remain alive.  So although there are great benefits from being a mammal, there can be disadvantages too.  In a sense no living animal is more "advanced" than any other, as we have all survived this far.  Adders must have many genes in common with us, because they have many of the same organs, and they have descended, like us, from four-legged animals.  We must in fact share a common ancestor with them. We have some concerns in common – we have to survive, eat and reproduce.  Nevertheless the adder is an alien creature.  We cannot share its world.

No mammals, even those who live underground, or seek prey which live underground, have become as long and thin as snakes.  One penalty paid by snakes for this shape is that the organs are long and thin, and undoubtedly less efficient than those of mammals.  For a mammal, such a shape would result in a much greater rate of loss of heat for a given mass, and the animal would need to carry more fat, carry more fur, or eat more, in order to maintain temperature, at least in a cold climate.  The first two methods would tend to negate the thinness, and the last is an obvious penalty.  Mustelids such as the stoat and the weasel seem to be about as far as the mammals have gone in this direction.  In fact, on average, the smaller a mammal, the more spherical it needs to be to conserve heat.  Is this borne out by the facts?

A snake swallows its prey whole, because it is not equipped with cutting teeth or chewing teeth, though it may possess small backward pointing ones.  By advancing different parts of its mouth in turn, the snake slowly engulfs the prey.  By taking the prey head first, the snake uses the the ratchet effect of the fur, as well as the ratchet effect of the teeth, to help in moving the animal back.  The teeth are not permanent: the snake drops them and grows new ones throughout its life.

Some snakes can find a mammal by detecting the infra-red radiation emitted by the warm body.  Of course, all objects emit this radiation all the time: the snake detects the difference between the animal’s emission and that from the surroundings.  Although the temperature difference is small, the rate of emission is a strong function of temperature, varying as the fourth power of the temperature.  A difference in temperature of 5 Celsius represents about 1.7 per cent on the absolute scale.  The difference in radiation emission might be four times as much as the temperature difference, about 7 per cent in the  example given.

When the adder is close enough to the prey, it strikes with the fangs, which are at the front of the mouth, injecting a lethal dose of venom down a canal in each fang.  The venom does not kill immediately, but the animal soon weakens and dies.  The adder has only to follow the scent and the warmth to find the dead animal.  Snake venoms are quite  complicated liquids, containing digestive enzymes as well as the venom.  The enzymes can greatly hasten decomposition of tissue.  Many of the venomous constituents work by interfering with nervous impulses; some degree of paralysis may result, as well as difficulty in breathing.  The venom may impede coagulation of the blood, and may affect the cardio-vascular system.

The fangs of some snakes have grooves to carry the venom, but in vipers the grooves have closed over to form a canal or tube.

Habitats

Adders can live in a wide range of habitats, being found further north than any other snake, even as far as the Arctic circle.  The further south they live the higher the ground they choose, so that they are always found at about the same temperature range.

Adders breeding

A good time to see adders is the breeding season.  The males become less timid, and can be followed for quite long distances as they seek the females. 

An adder leaves its hole to look for a female.

The journey can be arduous.

A female is basking          A male arrives    

How did he find her?  The male adder uses its tongue to test the air for the scent of a female.  The mouth is shaped so that the adder can put out its tongue though a little gap without opening its mouth.

In the next two pictures you can just about see the adder’s tongue. 

In the right hand picture the female’s head shows the slot for the tongue. 

If you decide to watch a male adder searching for a female, you may need great patience – they can seem very slow in finding a female which you yourself can already see.  But then, you aren’t half an inch from the ground.  When a male adder comes within sight of a female, what happens next depends on whether another male is already in attendance.

If another male is already present, the incoming adder will assess the situation carefully from a safe distance.  If the incumbent adder looks too big and strong, the new adder will quietly withdraw and go elsewhere, if possible without being detected.  If you stand quietly behind such an adder, you can almost see it thinking.  But if the other adder doesn’t look too big, the new adder will approach the pair.  Then you can see something which is not at all uncommon, but is rarely seen because most people have not looked for it.  This is the contest between male adders for possession of the female.  It is a competition rather than a fight. The adders never seem to open their mouths, let alone bite or use venom.

Competing adders

The adders rear up and push each other around, often twining around each other, in a wrestling match which looks sometimes looks rather ineffectual, but it can be surprisingly athletic.  The adders seem to be completely oblivious of their surroundings, allowing you a really good chance to observe them closely.  The first picture below was taken after the adders had been struggling together for over fifteen minutes.  They were clearly tired, and were losing interest.  Shortly after this they went their way, without an obvious winner emerging, and neither of them seemed to remember the female that had been the cause of the battle. 

If the adders are not well matched, one will quickly give in and slip away, chased by the winner until he is well away from the female.

Large JPEGs of Adder Contest

In the last picture, the winning male surveys the scene after seeing off the other male for the second time.  Occasionally the losing male does try to return to the scene, presumably to look for the female, but the winner always chases him away very quickly.

If there is no clear winner, an adder contest may go on for many minutes.  It may carry the males up to several metres away from the female as they wrestle and pursue. 

After a contest, the losing adder seldom returns, but if he does dare to reappear, the successful adder will be after him like a flash, and he will have to turn and get away at top speed.  In his panic he will go over everything in his path without stopping to check, including your foot.  After a contest the winning adder may take some time to find the female again, perhaps because there may be adder scent over all the places where she has been, making a confusing pattern.

If you watch the pair from this point on, you will then see how the male courts the female and excites her interest.  Sometimes she will glide along, with the male flowing around and over her in a way that is hard to describe, and impossible to forget.  Great coordination is necessary in the muscles, because some parts of the male are on the ground and some are on the moving female.  Snakes also cope very well when several are curled up together and they need to move.  They never seem to get in a muddle.

Here the male is trying to stimulate the female’s interest by gliding over her and making sudden little movements.  Eventually she may allow the male to couple with her. Once they have joined together, they may stay like that for an hour or more.  If you disturb them, the female will slide away, dragging the male backwards behind her. This must be uncomfortable if they go down a narrow hole.  So it is a good idea to keep your distance so as not to spoil their basking, as indeed it is at all times.

The next set of pictures was taken during a typical encounter between a male and a female.  The courtship had already begun when the adders were found.  After ten minutes or so, they were left to continue undisturbed.  In a small population, any disturbance in the reproductive cycle could be significant, especially as females breed only in alternate years at most.  Unfortunately, adder colonies in England tend to be small, and they are very vulnerable.  Killing a single animal, especially a pregnant female, could have a very bad effect.  Numbers vary noticeably from year to year, because the effects of predation and conditions.

After the mating the male may stay with the female for up to a week, but after that he will wander off to seek food.  So males may no longer be seen in the breeding area, but the females will go on basking.  Sometimes if you get too close during this time, the female will hiss rather than glide away when disturbed.

Females breed only in alternate years – sometimes even less frequently.  Perhaps this is because they carry their young until they are ready to live without help, which requires a lot of energy from the female.  She seldom catches prey during gestation.  Adders produce from four to ten young, the smaller numbers being more common.  Females reach sexual maturity at four to five years old, males a year younger.

Retaining the eggs until the hatch is an adaptation to cooler climates where there are not enough warm places to incubate them outside a body.  The extra bulk and weight makes life difficult for the pregnant female, who will have to feed on small prey because of the limited space available in her body, and will experience problems with mobility.

Contented  Couples

After mating, male and female may stay together for a long time, possibly up to a week.  After this period, the males tend to disappear, so that during the summer you are much more likely to see females than males.

Later in the summer you may be lucky enough to see the young adders as they bask in the sun, before they leave the place where they were born.  They are hard to see, being very small – no thicker than a pencil – and they tend to hide in little sun-traps. Just after their emergence, they may be seen in some numbers.  A few days later, when they have dispersed, they will be even harder to find.  They are quite difficult to photograph, for the same reasons.  Their colours do not seem to vary as much as those of the adults.  Many young adders are sandy to brownish in colour.

A few days after their birth, when they have dispersed, they will be even harder to find.   Here are adders which were less than a week old.

When the days become too cold, the adders will disappear below ground, and will probably not be seen again until the warm spring days, unless the winter includes some exceptionally warm days.

When you see a very young adder, and you compare it with an adult, you may find it difficult to believe that an adder can produce from four to ten young.  Let’s see whether this is reasonable.  Here are diagrams of an adult snake and two young ones.

The larger young one is a third the length and width of the big one: the ratio for the smaller one is a quarter.  The ratio in volumes between adult and young in the two cases is (1/3)³ and (1/4)³, that is 1/27 and 1/64 respectively.  If we assume ten young in each case, which is exceptionally high for an adder, the total volume of young will be 1/2.7 or 1/6.4 of the volume of the adult.  Let’s assume that the young are spread out along about a third of the length of the adult, remembering that all the organs of a snake are elongated.  

The ratios of the volumes of the young to this third of the adult will be 3/2.7 and 3/6.4, which are 1.11 and 0.47.  The new volume of that part of the adult will be increased in the ratio 1+1.11 and 1+0.47, that is, 2.11 and 1.47. To accommodate these volume increases, the radius of the adult will have to increase by the square root of these ratios, that is by the ratio 1.45 and 1.21.  These are not excessive values.  A pregnant adder does indeed look more plump than before, but not by a huge amount.  Nevertheless, you can easily recognize a pregnant female, and even by early July, a female adder can experience difficulty in moving, especially up a slope, and is unlikely to catch any prey.

The disadvantage of having to nourish little adders all the way through to the point where they can fend for themselves is a disadvantage to be weighed against the advantage to the young of being well protected during that time.  This burden is probably one reason that female adders do not breed in consecutive years.  The grass snake takes a very different route, laying a large number of eggs and leaving them to develop in a warm place, while the female is free to feed.

Adders, like many other animals, choose places that do not necessarily look attractive to us.  Tidying up the countryside to make it look more like a park is so inimical to the interests of many plants and animals that it should not be done without a great deal of circumspection.  Never move anything in order to find an adder. You may injure an adder, or you may inadvertently block an entrance if you replace a stone inexactly.  And of course you may be bitten.

All the adders in these pictures lived in a rectangle of no more than a square km.  In fact they were in several strips of ground no more than a few hundred metres long by 5 m to 10 m wide, a very small area.  Clearly they are vulnerable to changes in their small habitats.

If one segment of a spider web is removed, all the others will move slightly to a new equilibrium.  If one species is removed, all the others will adjust.  The loss of snakes from Great Britain might affect very few people and very few things; after all, they manage perfectly well in Ireland without any.  They would be missed only the people who care about them and enjoy watching them.

Adder  Facts

Animals which can glide gracefully along the ground, with no visible effort, climb, swim gracefully through the water, glide through the air and burrow; and envenomate or constrict; are bound to excite feelings of admiration, awe, fear or loathing, depending on the person and the culture in which he or she lives.  Even now, there are people who believe that snakes are slimy and disgusting.  Few of us are without a dislike of some animal.

Man’s relationship with animals and plants has been expressed in art, mythology and religion, from very early times.  A S Byatt’s book "Possession" includes a long poem about the Fairy Melusina, a creature who is part woman, part snake.  Like several other animals, snakes are included in a number of creation myths.

Vipers are responsible for three of Shakespeare’s most bizarre stage directions, in "Anthony and Cleopatra" – 

[To an asp, which she applies to her breast.  

[Applying another asp to her arm.  

[Applies an asp.  

These are followed shortly by –

[Dies.

Unfortunately, after this, a guard refers to the "trail of slime" left by a snake, which is of course nonsense.  Before the tragic scene, Cleopatra refers to the snake "that kills and pains not".  She was soon to find out that "pains not" was badly wrong.  Such was the state of knowledge of snakes.

In Act III of King Richard II, the King says – "O villains, vipers, damn’d without redemption!  Dogs, easily won to fawn on any man!  Snakes, in my heart-blood warm’d, that sting my heart!"

Near the end of "The Tragedy of Othello" we find –

Lodovico: Where is that viper? Bring the villain forth.    (Of Iago.)

In "The Tragedy of Macbeth" we find –

Macbeth: We have scotch’d the snake, not kill’d it.

Second Witch: Fillet of a fenny snake,    (Grass snake?)

In the cauldron boil and bake;

Eye of newt and toe of frog,

Wool of bat and tongue of dog,

Adder’s fork and blind-worm’s sting,    (Slow-worm has sight, but no venom.)

Lizard’s leg and howlet’s wing,

For a charm of powerful trouble,

Like a hell-broth boil and bubble.

In "Cymbeline" –

Pisanio: Maids, matrons, nay, the secrets of the grave

This viperous slander enters.     (Viperous here probably means poisonous.)

See also –

"Snake" by D H Lawrence which is analysed by Heather Haberl.

"The Viper" by Gavin Miller

"Snake" by Emily Dickinson

"The Diamondback" by J Copek

"Rattlesnake Dreams" by Ray Gonzalez

Children’s poems about snakes from Porchester School, Nottingham

"Sendin’ the Vipers" by Mezz Mezzrow and his Orchestra

"Chant for Killing a Snake" by Nicolas Guillen – Sensemaya – Eartha Kitt

The Singing Snake by Stefan Czernecki

Snake painting

Snakes and lizards were sacred to the Egyptian god Atum.  Apep was a serpent-god, as were Mehen, Nehebkau and Uto/Wadjet, and Hathor was often depicted as a snake, as were Tefnut and Uajyt.  Meretseger was a cobra-goddess.  Quetzalcoatl was one name of the central American feathered serpent-god.  In Japan, Benten, the love-goddess, was associated with the snake and the dragon.

If you type "snake.god" in the search box of Google you will find a number of references to books and films.

Near the beginning of the Jewish Torah and the Christian Old Testament, the snake is portrayed a tempter.  From the RSV bible –

Then the Lord God said to the woman, "What is this that you have done?"  The woman said, "The serpent beguiled me, and I ate."  The Lord God said to the serpent, "Because you have done this, cursed are you above all cattle, and above all wild animals; upon your belly you shall go, and dust you shall eat all the days of your life."

Much later, we find this –

Moses and Aaron went to Pharaoh and did as the Lord commanded; Aaron cast down his rod before Pharaoh and his servants, and it became a serpent.

And in the Book of Proverbs –

Three things are too wonderful for me;

four I do not understand:

    the way of an eagle in the sky,

    the way of a serpent on a rock,

    the way of a ship on the high seas,

    and the way of a man with a maiden. 

Saint Patrick is said to have had the authority to have the snakes driven out of Ireland, as a symbol of his power over evil.  The picture in this link shows a snake.  In another version of the legend, the snake is a pagan symbol.

The western basilisk and dragon are more recent developments.  Greek mythology includes the nine-headed Hydra and the Medusa, with a head covered in snakes.  In Walt Disney’s "Jungle Book", in the song "Trust in Me", the snake is a wily, untrustworthy character.  We still sometimes use the phrase "snake in the grass", though in fact snakes are probably no more untrustworthy than chaffinches, chinchillas or chimpanzees.  The concepts of conscious deceit and honesty probably require high intelligence.

Sometimes we associate honesty with words such as "straight" and "upright".  We can be exhorted to "walk tall" and "keep your chin up".  What could be more different from these ideas than a creature that lies on the ground and is "bent" or "crooked", words we use to denote dishonesty.  The word "insinuate", coming from the same root as "sinuous" and "sine", also implies deviation from the straight and narrow, like the word "devious".  We refer to some people as "creeping" or "crawling", more pejorative words.  "Low cunning" has the same kind of connotation.

Baden-Powell’s book "Scouting for Boys" included pictures of a smoker and a non-smoker.  The non-smoker was a an upright blond youth, chest thrust out, back ramrod straight.  The smoker, cigarette dangling from lower lip, was portrayed as a skinny person with a hollow-chested profile and a curved spine, almost a parody of the S-curve use to portray elegant ladies in Japanese prints.

In "Harry Potter and the Philosopher’s Stone", J K Rowling seems to remain true to the same image of snakes.  Of the four houses in Hogwarts, the one associated with cunning has a name that seems to hint at both "sly" and "slither".  If you haven’t read the book, you can probably guess which animal is the symbol of the house.  And the name of the teacher who apparently dislikes Harry Potter seems to be an amalgam of "snake" and "snipe".  Do snakes appear elsewhere in the Harry Potter books?

Snakes and dragons are sometimes seen as the guardians of treasures, as recently as J R R Tolkiens’ book "The Hobbit", in which the dragon, Smaug, is deprived of the Arkenstone, a great gem, provoking great anger in Smaug, who comes out of the mountain to attack a town.  In "The Lord of the Rings", the name Wormtongue is based on the old use of "worm" for a serpent.

On a lighter note, in the game of Snakes and Ladders, it is the snakes that send you backwards towards the start.

The snake has been seen as a medicinal symbol, for example as Asklepios or Aesculapius.

See "Snakes – A Natural History", edited by Roland Bauchot, for much more information on this subject, as well as on the lives of snakes.

Egyptian gods – Apep Atum Hathor Mehen Meretseger Nehebkau Tefnut Uajyt Uto/Wadjet     Degei – Fijian snake-god     The serpent as divinity

Quetzalcoatl – feathered serpent    Teotihuacan – serpent god

Sumerian serpent god

Where snakes live

Snakes live between snail and snap, in an English dictionary, and these are surrounded by many other words beginning with "sn".

Let’s make some lists –

snap-dragon   snazzy   snog   snug

snack   snaffle   snap   snap-fastener   snapper   snapping turtle   sneeze   snip   snipe   snood  snooker   snooze   snorkel   snort   snout   snow   snuff   snuffle   snuggle

snag   snaggle-tooth   snap   snare   snarl   snatch   sneak   sneer   sniff   sniffy   snigger   snipe   snitch   snivel   snook   snoop   snooty   snore   snort   snub

It has been said that words beginning with "sn" tend to have negative connotations.  The three lists attempt to group the words into positive, neutral and negative, respectively.  Do you agree?  Is this significant?  Are these words derived mainly from French or Latin, or from other sources?

Two English land animals have names beginning with sn – snail and snake.  The English could have chosen a French derivation, as they did with many other words, and called them escargot and serpent.

Photographing Adders    Adder Links

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